netdev - RE: Ethernet TX buffer crossing 4K boundary?

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Message-ID: <5f7abe88a55a40d9a6a7f03f9c6af48c@AcuMS.aculab.com>
Date:   Thu, 21 Apr 2022 13:39:37 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Andrew Lunn' <andrew@...n.ch>,
        Joakim Tjernlund <Joakim.Tjernlund@...inera.com>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Eric Gratorp <Eric.Gratorp@...inera.com>
Subject: RE: Ethernet TX buffer crossing 4K boundary?

From: Andrew Lunn
> Sent: 21 April 2022 13:33
> 
> On Wed, Apr 20, 2022 at 09:09:58PM +0000, Joakim Tjernlund wrote:
> > We have this custom Ethernet controller that cannot DMA a buffer if the buffer crosses 4K boundary.

Fix the hardware :-)

> > Any ideas how to deal with that limitation in the driver?
> 
> Does the DMA support scatter gather? You might be able to tweak the
> generic scatter gather code to generate two blocks if it crosses the
> boundary.

I'd also look at the USB3 xhci code.
That also has a perverse set of restrictions on buffer alignment.
Might give you some hints.

	David

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